<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>9-9练习</title>
</head>
<body>
    <script>
        // alert('Hello javaScript');
        // console.log('Hello javaScript');
        // prompt('Hello javaScript');
        var left ="刀";
        var right ="又"
        var temp =""
        document.write("left ="+ left + "<br>"),
        document.write("right="+ right + "<br>");
        document.write("--<br>");

        temp = left;
        left = right;
        right = temp;
        
        document.write("left="+ left + "<br>");
        document.write("right="+ right + "<br>");
    </script>
</body>
</html>